1. Field of the Invention
This invention relates to a photoconductive member having sensitivity to electromagnetic waves such as light (herein used in a broad sense, including ultraviolet rays, visible light, infrared rays, X-rays, gamma-rays and the like).
2. Description of the Prior Arts
Photoconductive materials, which constitute image forming members for electrophotography in solid state image pick-up devices or in the field of image formation, or photoconductive layers in manuscript reading devices, are required to have a high sensitivity, a high SN ratio (Photocurrent (I.sub.p)/Dark current (I.sub.d)), spectral characteristics matching to those of electromagnetic waves to be irradiated, a rapid response to light, a desired dark resistance value as well as no harm to human bodies during usage. Further, in a solid state image pick-up device, it is also required that the residual image should easily be treated within a predetermined time. In particular, in case of an image forming member for electrophotography to be assembled in an electrophotographic device to be used in an office as office apparatus, the aforesaid harmless characteristic is very important.
From the standpoint as mentioned above, amorphous silicon (hereinafter referred to as a-Si) has recently attracted attention as a photoconductive material. For example, German Laid-Open Patent Publication Nos. 2746967 and 2855718 disclose applications of a-Si for use in image forming members for electrophotography, and German Laid-Open Patent Publication No. 2933411 an application of a-Si for use in a photoconverting reading device.
However, under the present situation, the photoconductive members having photoconductive layers constituted of a-Si are further required to be improved in a balance of overall characteristics including electrical, optical and photoconductive characteristics such as dark resistance value, photosensitivity and response to light, etc., and environmental characteristics during use such as humidity resistance, and further stability with lapse of time.
For instance, when applied in an image forming member for electrophotography, residual potential is frequently observed to remain during use thereof if improvements to higher photosensitivity and higher dark resistance are scheduled to be effected at the same time. When such a photoconductive member is repeatedly used for a long time, there will be caused various inconveniences such as accumulation of fatigues by repeated uses or so-called ghost phenomenon wherein residual images are formed, or when it is used at a high speed repeatedly, response is gradually lowered.
Further, a-Si has a relatively smaller absorption coefficient in the wavelength region longer than the longer wavelength region side in the visible light region as compared with that on the shorter wavelength region side, and therefore in matching to the semiconductor laser practically used at the present time or when using a presently available halogen lamp or fluorescent lamp as the light source, there remains room for improvement in that the light on the longer wavelength side cannot effectively be used.
Besides, when the light irradiated cannot sufficiently be absorbed into the photoconductive layer but the dosage of the light reaching the support is increased, if the support itself has a high reflectance of the light permeating through the photoconductive member, there will occur interference due to multiple reflections which may be a cause for formation of "unfocused image".
This effect becomes greater, if the spot irradiated is made smaller in order to enhance resolution, and it is a great problem particularly when using a semiconductor laser as light source.
Further, a-Si materials may contain as constituent atoms hydrogen atoms or halogen atoms such as fluorine atoms, chlorine atoms, etc. for improving their electrical, photoconductive characteristics, boron atoms, phosphorus atoms, etc. for controlling the electroconduction type as well as other atoms for improving other characteristics. Depending on the manner in which these constituent atoms are contained, there may sometimes be caused problems with respect to electrical, photoconductive characteristics of the layer formed.
That is, for example, in many cases, the life of the photocarriers generated by light irradiation in the photoconductive layer formed is insufficient, or at the dark portion, the charges injected from the support side cannot sufficiently be impeded.
On the other hand, in view of matching to semiconductor laser, it has also been proposed to provide a light receiving layer constituted of an amorphous material containing at least germanium atoms. However, in this case, problems are sometimes involved in adhesion between the support and the light receiving layer and diffusion of impurities from the support to the light receiving layer.
Thus, it is required in designing of a photoconductive material to make efforts to overcome all of the problems as mentioned above along with the improvement of a-Si materials per se.
In view of the above points, the present invention contemplates the achievement obtained as a result of extensive studies made comprehensively from the standpoints of applicability and utility of a-Si as a photoconductive member for image forming members for electrophotography, solid state image pick-up devices, reading devices, etc. It has now been found that a photoconductive member having a layer constitution of photoconductive layer comprising a light receiving layer exhibiting photoconductivity, which is constituted of so-called hydrogenated amorphous silicon, halogenated amorphous silicon or halogen-containing hydrogenated amorphous silicon which is an amorphous material comprising a-Si, especially silicon atoms as a matrix and at least one of hydrogen atom (H) and halogen atom (X) (hereinafter referred to comprehensively as a-Si(H,X)), said photoconductive member being prepared by designing so as to have a specific structure as hereinafter described, is found to exhibit not only practically extremely excellent characteristics but also surpass the photoconductive members of the prior art in substantially all respects, especially having markedly excellent characteristics as a photoconductive member for electrophotography as well as excellent absorption characteristics on the longer wavelength side. The present invention is achieved based on such finding.